A knock on the door interrupts Marty (James Franco), a minor entrepreneur of teen porn. in the middle of a photo session. His visitor, Richard Kuklinski (Michael Shannon), has come to kill him. When he sees Marty clasping his hands, Kuklinski instructs him to pray to God to save him. Silence from above. “I think God’s busy, Kuklinski whispers. Blam!

Cowering in the closet is the 17-year-old girl Marty was photographing. Kuklinski lets her go. “I don’t kill women and children,” he explains later. Even in the ninth circle of the New Jersey underworld, a man can have ethics. Question is, given the volatility of his employer, can he afford them?

The Iceman, from the Israeli-born director Ariel Vromen, is a B movie and proud of it. Based on Kuklinski’s more-or-less true story — after his 1986 arrest he claimed to have committed more than 100 murders, maybe as many as 250 — this Mafia tale doesn’t aspire to the heights of a Godfather, the epic sprawl of The Sopranos. Vromen and cowriter Morgan Land are content to bring familiar shades to the tale of a strange man in a dirty business. The Iceman presents but does not explain Kuklinski, leaving Shannon to dominate the character by his quiet, creepy presence.

The craziest thing about Kuklinski is his devotion to his wife Deborah (Winona Ryder). When they meet, in 1964, tells her she’s “a prettier version of Natalie Wood.” He may believe it. Over the nest two decades he will do anything for Deborah and their two daughters, who (the movie says) know nothing of his real business. He says his job is “currency valuation,” which is true insofar as he values the currency he gets from killings to support his family. He’s also not lying when he tells Deborah, “You and the girls. That’s all I care about in the whole f—in’ world.” In a killer, a soft heart is a soft spot, a weakness his enemies can exploit.

Kuklinski doesn’t feel a similar sentiment for his victims, whom in his first three killings he dispatches with a knife, a gun and an ice pick. His expertise has attracted the interest of crime boss Roy Demeo (Ray Liotta), Roy gratefully puts Kuklinski to work reducing the population of Jersey wise guys and increasing the body count. But when Roy’s fidelity to a reckless underling (David Schwimmer) forces him to lie low, the contracts stop and Kuklinski is out of work. So the Polish-Irish killer pairs with the Dutch-Irish Robert Pronge (Chris Evans), whose cover job running an ice-cream truck has earned him the nickname “Mr. Freezy,” to do freelance killings, putting the corpses on ice until they can be chopped up and substituted for more recent crime victims. That sideline won’t last forever.

Actors love to play against type, and among the amusements of The Iceman is the spectacle of Friends schlub Schwimmer as a dopey mobster and Captain America Evans as the cyanide-wielding Freezy. Other actors happily exploit the types they’ve been playing their whole careers: Liotta the shifty Mafioso, and Robert Davi as a wise old consiglieri who blithely advises Kuklinski that “Life is random.” Translation: you’d better buy bullet-proof vests for your wife and kids.

Shannon, of course, is the story here. Indie films’ favorite neurotic in Revolutionary Road and Take Shelter, he rarely raises his voice here. Doesn’t need to; if looks could kill, everyone in the movie would be dead. Everyone watching, too. Occasionally, Shannon’s gun-metal gaze catches the camera’s eye, and he stares it down as if to say, “What are you lookin’ at?” If The Iceman gets an official release this year, after playing here and at the Toronto Film Festival, Shannon could be looking at an Oscar nomination. His performance is that stone-cold good.